1. Field of the Invention
The present invention relates to a wired circuit board and to a producing method thereof. More particularly, the present invention relates to a wired circuit board having a terminal portion to be connected with external terminals and to a producing method thereof.
2. Description of the Prior Art
The wired circuit board usually has a conductive pattern configured by a plurality of lines of wire formed on an insulating base layer and further has an insulating cover layer formed on the insulating base layer to cover the conductive pattern.
This wired circuit board has a terminal portion formed in the conductive pattern to be connected with external terminals of an electronic component and the like. The insulating cover layer is formed to have an opening formed to correspond to the terminal portion so that the terminal portion can be exposed from the opening to connect with the external terminals.
Accordingly, positional precision of the relative position of the terminal portion with the opening and dimensional precision of the opening are critical for connecting the terminal portion with the external terminals with high precision.
There are three known methods for forming the insulating cover layer to have the opening in it, as outlined below. The first method is a method using a screen printing method in which a solder resist is formed to form the opening in the insulating cover layer. The second method is a method in which an insulating resin film with a preformed opening is adhesively bonded to form the opening in the insulating cover layer, or a method in which an insulating resin film is adhesively bonded, first, and, then, the opening is formed in the insulating resin film. The third method is a method using photolithography in which after coated, photosensitive resin is exposed to light and developed to form the opening in the insulating cover layer.
However, the first method has the problem that when printed (coated), solder resist 30 may flow into between lines of wire 34 at the terminal portions 33 exposed from the opening 32 of the insulating cover layer 31 due to the capillary phenomenon until it reaches an electronic component mounting place 35 where the terminal portion 33 is connected with the external terminals, as shown in FIG. 14. In this case, it becomes difficult to mount the electronic component to connect the external terminals with the terminal portion 33.
The second method has the problem that an adhesive may flow into between the lines of wire 34 due to the capillary phenomenon until it reaches the electronic component mounting place 35 where the terminal portion 33 is connected with the external terminals, as is the case with the first method. In this case also, it becomes difficult to mount the electronic component to connect the external terminals with the terminal portion 33.
The third method has the problem that when a photo mask is out of position in the process of the photolithography, the electronic component mounting position 35 may be covered with the insulating cover layer 31, as shown in FIG. 15. In this case also, it becomes difficult to mount the electronic component to connect the external terminals with the terminal portion 33.
The prior art proposes solution that the lines of wire at the terminal portion are machined using a bending or pressing process to provide e.g. an indented surface to make it hard for the solder resist to flow out, so as to prevent the solder resist printed from flowing out to a device hole side (Cf. JP Laid-open (Unexamined) Patent Publication No. 2003-309 148, for example).
However, the provision of the indented surface for the line of wire by the machining process requires a cumbersome and complicated work, causing reduction in workability and increase in cost.
Also, it is usual that whether or not the insulating cover layer reaches the electronic component mounting place is determined by a continuity test after the mounting of the electronic component or by measurement of a dimension of the insulating cover layer flown in between the lines of wire at the terminal portions. However, such an inspection carried out during the production process makes it hard to provide cost reduction while ensuring high productivity.